program vpkl;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
  n,f,s,d,i:Integer;
  massX: array of Integer;
  massY: array of Integer;
begin
  readln(n);
  d:=0;
  setlength(massX,n);
  setlength(massY,n);
  For i:=0 to n-1 do
    readln(massX[i],massY[i]);
  i:=0;
  F:=massX[i]*massY[i+1]-massx[i+1]*massY[i]+massX[i+1]*massY[i+2]-massx[i+2]*massY[i+1]+massX[i+2]*massY[i]-massx[i]*massY[i+2];
  For i:=1 to n-3 do
    begin
      S:=massX[i]*massY[i+1]-massx[i+1]*massY[i]+massX[i+1]*massY[i+2]-massx[i+2]*massY[i+1]+massX[i+2]*massY[i]-massx[i]*massY[i+2];
      If F*S<0 then
        d:=1;
      F:=S;
   end;
   i:=n-2;
   S:=massX[i]*massY[i+1]-massx[i+1]*massY[i]+massX[i+1]*massY[1]-massx[1]*massY[i+1]+massX[1]*massY[i]-massx[i]*massY[1];
      If F*S<0 then
        d:=1;
      F:=S;

   i:=n-1;
    S:=massX[i]*massY[1]-massx[1]*massY[i]+massX[1]*massY[2]-massx[2]*massY[1]+massX[2]*massY[i]-massx[i]*massY[2];
      If F*S<0 then
        d:=1;
      F:=S;
  If d=1 then
    Writeln('no')
  Else
    Writeln('Yes');

  Readln;
end.

